Manta ray nursery discovered off Palm Beach County coast
A nursery for giant oceanic manta rays has been discovered in the saltwater border of Palm Beach County in a study scientists say is a first step to protecting what could be critical habitat for the threatened species.
Three years of continuing research of coastal waters largely from the Jupiter Inlet to the Boynton Inlet found an unusual number of juvenile manta rays gliding through shallow waters sometimes just feet from swimmers.
The gentle ocean megafauna feed on tiny zooplankton, funneling water into their mouth with two horn-like fins on either side of their head, and are no threat to humans. They do not have barbed tails like stingrays.
Jessica Pate, whose study on the manta ray nursery was published this month in the journal Endangered Species Research, is also founder and lead scientist for the Florida Manta Project.
She said it wasn’t a shock to find the inquisitive ocean titans along Palm Beach County’s coast, but it was a surprise to find only young ones.
“We don’t know exactly why they are choosing this area as a nursery,” said Pate, who earned a master’s degree in biology from Florida Atlantic University. “Typically, nurseries are chosen because there is a lot of food or a lack of predators so they can grow safely.”
At birth, giant oceanic manta rays are as big as 6-feet across — coming into the world folded up like a “manta ray burrito”, Pate said.
As adults, they can grow to 23 feet with gaping pectoral wings, cutting silently through tropical waters like wraiths.
“People will go halfway across the world just to dive with manta rays,” Pate said. “They can be very curious and we think they are likely very smart. We definitely see different personalities.”
Some of Pate’s manta rays were seen frequently enough they earned names such as sky, Ricky and Stevie Nicks – a moniker given by an intern who had been listening to Fleetwod Mac the night before.
Sharks and rays, including the more commonly sighted spotted eagle rays, are related in that their skeletons are made of pliable cartilage rather than bone.
“Think of a shark under a steam roller and flattened out and then you have a ray,” said Stephen Kajiura, director of FAU’s Elasmobranch Laboratory.
Kajiura does aerial surveys of the blacktip shark migration along Palm Beach County’s coast and would text Pate whenever he saw a manta ray in the water.
Her study, which was co-authored by Marine Megafauna Foundation co-founder Andrea Marshall, identified 59 individual manta rays, the majority of which were juveniles based on sexual maturation and size. Many showed signs of human-caused injuries from fishing hooks, fishing line or gashes from boat propellers.
Calusa Horn, the National Oceanic and Atmospheric Administration’s giant manta ray recovery coordinator in the Southeast region, said little is known about oceanic manta rays.
Aside from a 1998 paper documenting the sighting of three manta rays in the Indian River Lagoon, Pate’s paper is the first study of manta rays in Florida, according to her research.
Manta rays weren’t listed as federally threatened until 2018, which may be one reason for a lack of research, Horn said. Marshall, Pate’s co-author, was the first person to earn a Ph.D. studying manta rays in 2008.
Manta rays’ gill plates, which the animal uses to trap plankton, are valued in traditional Chinese medicine. That makes them a target for fishermen in the gill plate trade, and vulnerable to extinction. Manta rays have lower reproductive rates, staying pregnant for a full year and producing just one pup every two to five years.
“We’re finding out more and Jessica’s work is helping us figure out what manta rays are doing in the Southeast,” Horn said. “Manta rays are largely considered deepwater animals and are highly migratory. Outside of Jessica’s area, we are not aware of any area where they are coming so close to shore.”
Palm Beach County’s proximity to the Gulf Stream current — a warm water highway going north that can teem with fish hitching rides on the flow — could be one reason for a nearby manta ray nursery, Horn said.
NOAA is working with Pate to tag Palm Beach County’s manta rays with satellite trackers to get a better idea of where they are going. The information can be used to develop a management plan for the manta rays as well as put protective measures in place if necessary.
“Unless we have the kind of baseline data Jessica is providing you are shooting blind,” Kajiura said. “I think it’s amazing how we have these huge rays so close to the beach, and here we are in one of the most densely populated parts of Florida.”